If the fan won't start up it will not turn on. I would check the voltage coming into the fan first. Are your batteries good or are you plugged into an electrical hookup? Bet you can guess I had the same problem and it was because the fan was not getting a full 12 volts.

You can do a continuity test on the thermostat. It is just a switch. Or you can bypass it and see if the system fires up.

If the fan comes on, but furnace won't fire, it's most likely a low-voltage issue. The fan needs to be up to speed to trip the sail switch. If the fan is dirty, it may not move enough air to trip the sail switch.

Let us know what the symptoms are, and I'll bet you will get some expert advice on here.

I just ordered a new relay board for my ac unit. In my case, my fan runs even when the thermostat is "off". It doesn't respond to any of the controls so neither the ac compressor or furnace will come on. The only way to shut it down is by switching the breaker off. Your's could just as easily be a relay either stuck in the off position or blown altogether.

my fathers camper has heater failed a couple times over 15 years, each time turns out to be ckt board issue. Most RV places will replace and groom the new boards. I just dropped off the heater, which comes out easily. Cap off your gas line and camper still works fine for summer camping till it is fixed.

My camper is brand new and heat won't kick on either, but I'm not too worried about it because the temp is so hot in there, it's way above max setting on the thermostat, I'm sure once it cools down outside it will kick on. I'm not saying that's your issue but maybe.

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“Always do what is right. It will gratify half of mankind and astound the other.”

Not sure what the heat exchanger is in your I have one that has a cast iron exchanger and with the moisture in Propane after a while it ends up with rust in it so has to be removed and shaken out. Once it's clear runs like a champ.

Not sure what the heat exchanger is in your I have one that has a cast iron exchanger and with the moisture in Propane after a while it ends up with rust in it so has to be removed and shaken out. Once it's clear runs like a champ.

That is scary, please make sure you have a CO detector in your RV that works.